Sparing the Ortho-position in Nucleophilic Aromatic Substitution-Specific Displacement of the 4-SePh Group in 2,4-Bis(phenylseleno)nitrobenzene

Article abstract of DOI:10.1002/hc.20519

Upon treatment of o- and p- (phenylseleno)nitrobenzenes with sodium methoxide quantitative exchange reactions took place, affording the corresponding methoxynitrobenzenes. Upon reaction between 2,4-bis(phenylseleno) nitrobenzene 2 and sodium methoxide, an unusual regiopure formation of 4-methoxy-2-(phenylseleno)nitrobenzene 3 was observed. This product remained unreactive toward an excess of sodium methoxide, thus preventing the formation of 2,4-dimethoxynitrobenzene 6. The nature of the reactants and of the intermediate Meisenheimer complexes was examined by synthetic investigations, x-ray crystallography, and DFT calculations. We found that the observed selectivity can be understood in terms of traditional resonance considerations.

Full text of DOI:10.1002/hc.20519

Heteroatom Chemistry
Volume 20, Number 2, 2009
Sparing the Ortho-position in Nucleophilic
Aromatic Substitution-Specific
Displacement of the 4-SePh Group in
2,4-Bis(phenylseleno)nitrobenzene
Nicolai Stuhr-Hansen,1 Thorstein Finn Go¨tze,2 Lars Henriksen,2
Theis Ivan Sølling,2 Annette Langkilde,2
and Henning Osholm Sørensen3
1Department of Medicinal Chemistry, University of Copenhagen, Universitetsparken 2,
DK-2100 Copenhagen East, Denmark
2Department of Chemistry, University of Copenhagen, Universitetsparken 5,
DK-2100 Copenhagen East, Denmark
3Center for Fundamental Research: Metal Structures in Four Dimensions, Risø National
Laboratory for Sustainable Energy, Technical University of Denmark, Frederiksborgvej 399,
P.O. 49, DK-4000 Roskilde, Denmark
20:101–108, 2009; Published online in Wiley InterScience
ABSTRACT: Upon treatment of o- and p-
(www.interscience.wiley.com). DOI 10.1002/hc.20519
(phenylseleno)nitrobenzenes with sodium methoxide
quantitative exchange reactions took place, afford-
ing the corresponding methoxynitrobenzenes. Upon
reaction between 2,4-bis(phenylseleno)nitrobenzene 2
and sodium methoxide, an unusual regiopure forma-
INTRODUCTION
The phenylselenide ion has been intensively used as
a tool in organic synthesis [1] since it is a power-
ful nucleophilic species sufficiently reactive to ef-
fect nucleophilic aromatic substitution [2], a central
route to selenium containing materials. Recently, in
a study of the reactivity of halonitrobenzenes toward
the phenylselenyl anion, sodium phenylselenide was
prepared by rapid and precise reduction of diphenyl
diselenide with hydrazine-sodium methoxide [3]. By
addition of an excess of sodium methoxide to the
reaction mixture, a regiopure product, 4-methoxy-2-
(phenylseleno)nitrobenzene 3, formed and remained
stable even in the presence of a large excess of
sodium methoxide. The present paper addresses
the mechanistic reasons for the selectivity of the
reaction.
tion of 4-methoxy-2-(phenylseleno)nitrobenzene 3 was
observed. This product remained unreactive toward
an excess of sodium methoxide, thus preventing the
formation of 2,4-dimethoxynitrobenzene 6. The na-
ture of the reactants and of the intermediate Meisen-
heimer complexes was examined by synthetic investi-
gations, x-ray crystallography, and DFT calculations.
We found that the observed selectivity can be un-
derstood in terms of traditional resonance consider-
ꢀ
C
ations. 2009 Wiley Periodicals, Inc. Heteroatom Chem
Correspondence
to:
Nicolai
Stuhr-Hansen;
e-mail:
nsh@farma.ku.dk.
c
ꢀ
2009 Wiley Periodicals, Inc.
101

102 Stuhr-Hansen et al.
SCHEME 1
RESULTS AND DISCUSSION
under these circumstances decomposition reactions
such as demethylations were observed in GC-MS.
Regiospecific Isolation of
4-Methoxy-2-(phenylseleno)nitrobenzene
Investigations of the Reactivity of
(Phenylseleno)nitrobenzenes Toward
Methoxide Attack
Not surprisingly, 2,4-dibromonitrobenzene
1
smoothly reacted at room temperature affording
2,4-bis(phenylseleno)nitrobenzene 2 without de-
tectable by-products (Scheme 1). The yield was only
limited by losses during work-up. However, the re-
action between 2,4-bis(phenylseleno)nitrobenzene
and 1 equivalent of methoxide substitution occurred
only on the 4-position. 4-Methoxy-2-(phenylseleno)
nitrobenzene 3 was formed in a completely regiop-
ure fashion without sign of the other possible isomer
2-methoxy-4-(phenylseleno)nitrobenzene 5. Even
upon addition of a large excess (2.5–10 equivalents)
of methoxide, there was no sign of the double-
substituted product 2,4-dimethoxynitrobenzene
6. The substitution pattern of 3 was confirmed
since an unequivocal synthesis from 2-bromo-4-
methoxynitrobenzene 5 and sodium phenylselenide
yielded an identical product.
To obtain more information about the nature
of the regiospecific exchange of the phenylse-
lenyl group para to the nitro group, we made
individual comparisons between the reactivities
of phenylselenyl groups ortho and para to nitro
groups by reacting 2-(phenylseleno)nitrobenzene 7
and 4-(phenylseleno)nitrobenzene 9, respectively,
with sodium methoxide. In both cases, a fast ex-
change and quantitative reaction occurred lead-
ing to 2-methoxynitrobenzene 8 (Scheme 2, A)
It was clear that the methoxide anion specifi-
cally attacked the phenylselenyl group para to the
nitro group, and furthermore was unable to replace
a second PhSe group after introduction of the first
MeO-group. At elevated temperatures, it was pos-
sible to observe two entering methoxy groups, but
SCHEME 2
Heteroatom Chemistry DOI 10.1002/hc

Sparing the Ortho-position in Nucleophilic Aromatic Substitution 103
and 4-methoxynitrobenzene 10 (Scheme 2, B),
respectively. These results show that it is the pres-
ence of a PhSe group that renders the PhSe group
in the 2-position of 3 inert. The nitro-group might
direct the initial attack, but it is not responsible for
the inertness of the 2-PhSe group.
ortho-arylseleno substituent was evidenced by crys-
tal structures of 7 and 11 as shown in Fig. 1. The
˚
nonbonded Se· · ·O distance is 2.6517(13) A in 7 and
only slightly longer in 11 (2.6780(17) and 2.6732(18)
˚
A). This is significantly shorter than the sum of
˚
van der Waals radii (3.42 A). A search of the
Cambridge Structural Database [4] (version 5.29,
November 2007) shows that this trend is common
for all types of ortho-selenenyl substituted nitroben-
zenes [5]. (The lengths of the Se· · ·O interactions
in nine reported similar structures are in the re-
Crystal Structures of Ortho-Phenylselenylated
Nitrobenzenes
Unfortunately, crystals of 3 could not be prepared
in a quality suited for single crystal X-ray diffrac-
tion. However, high-quality crystals of similar or-
tho phenylselenylated nitrobenzenes of 7 and 1,3-
dinitro-4,6-bis(phenylseleno)benzene 11 (prepared
using standard conditions from 1,3-dibromo-4,6-
dinitrobenzene) suitable for X-ray structure deter-
mination were prepared, and their crystal structures
were determined. The structures (Fig. 1) will be com-
pared with related compounds found in the liter-
ature to provide additional information about the
exact geometries of the reaction centers during the
observed phenylselenyl exchange reactions.
˚
gion 2.3–2.7 A.). The consequence of this unusually
strong interaction between a selenium atom and an
ortho nitro group on a benzene ring reveals itself in
the unique stabilization of o-nitrobenzeneselenenic
acid [6], which is the only stable selenenic acid re-
ported. This ortho stabilization of the PhSe group
might be one of the keys to the exclusive attack on
the 4-position of 2,4-bis(phenylseleno)nitrobenzene.
Comparison of the X-ray Crystal Structure and
the Calculated Geometry of o-PhSe-C6 H4NO2 (7)
A strong through-space interaction between the
O-atom of the nitro group and the Se-atom of an
A strong interaction between the oxygen of the ni-
tro group and the selenium in the ortho position
FIGURE 1 ORTEP II drawings showing the structure and atomic labeling of (1) compound 11 and (2) 7. The thermal ellipsoids
are drawn at 50% probability and the hydrogen atoms as spheres with an arbitrary radius.
Heteroatom Chemistry DOI 10.1002/hc

104 Stuhr-Hansen et al.
FIGURE 2 Calculated geometries (B3LYP/6–31G(d)) of o-(phenylselenonitro)benzene 7 in two different conformations to-
gether with the para-isomer in the lowest energy conformation.
was found by X-ray crystallography with a distance
between the oxygen and the selenium of only
˚
2.6517(13) A as indicated in Fig. 1. This value agrees
˚
well with the distance of 2.60 A obtained at the
B3LYP/6–31G(d) level of theory and since a regu-
˚
lar Se O bond distance is of the order of 1.68 A [7].
No indication of a formal chemical bond between
the nitro group and the PhSe group was found. The
agreement between the calculated geometry and the
experimental structure seems to apply for most of
the structural parameters. The torsional angles as-
sociated with the nitro group are in both cases close
to 0◦, and in both cases the planes defined by the
phenyl groups are perpendicular (more so in the case
of the calculated geometry (92◦), than in the case of
the experimental structure (102◦)).
FIGURE 3 Calculated geometries (B3LYP/6–31G(d)) of the
nitroso compounds that would result from the transfer of an
oxygen atom from the nitro group to the selenium atom. The
lowest energy conformer lies 22.3 kcal mol−1 higher in energy
compared to the nitro-compound.
transfer of an oxygen atom from the nitro group
to the PhSe group, resulting in the formation of
a selenoxide with a nitroso substituent. The calcu-
lated geometry of this compound is shown in Fig. 3.
It lies substantially higher in energy (by 22.3 kcal
mol−1), and the formation of the nitroso compound
in Fig. 3 does therefore seem very unlikely even in
the case of a strong NO2–SePh interaction. The ni-
troso compound does also exist in two conformers
of very different stability (Fig. 3). One has the Se O
bond pointing away from the nitroso group. This
gives rise to a stabilization of 7.7 kcal mol−1 because
of the dipole–dipole stabilization that results from
having the dipolar groups Se O and N O pointing
in different directions as indicated in Fig. 3.
Relative Energies of a Series of PhSeC6 H4NO2
Isomers
In the attempt to locate a global minimum structure
of o-PhSe-C6H4NO2 a high-energy conformer (by
5.4 kcal mol−1) was identified, where the nitro group
is highly distorted away from the plane of the phenyl
group. In this geometry, the PhSe group points away
instead of pointing along the main phenyl group.
Both conformers are shown in Fig. 2. The ortho and
the para isomers are roughly equally stable, at the
B3LYP/6–31G(d) level, with the para isomer having
slightly lower energy by 0.6 kcal mol−1. This indi-
cates that the interaction between the PhSe group
and the nitro group only just overcomes the steric
repulsion between the ortho substituents. The cal-
culated geometrical features of the para isomer are
similar to those of the ortho isomer. The geometry
of the para isomer is included in Fig. 2.
Nucleophilic Aromatic Substitution:
The Meisenheimer Complexes
We have calculated the geometries of the
Meisenheimer complexes that would result from
nucleophilic attack of hydrogen selenide on both
A strong interaction between the nitro group
and the PhSe group could lead to a (hypothetical)
Heteroatom Chemistry DOI 10.1002/hc

Sparing the Ortho-position in Nucleophilic Aromatic Substitution 105
SCHEME 3
of the Mulliken charges. In the case of 2,4-
diphenylselenonitrobenzene, the results can be
taken to indicate that the amount of positive charge
at C2 is about half of the positive charge on C4,
making the attack of a nucleophile much more
attractive at C4. The fact that it is much more favor-
able for the molecule to position a higher degree of
positive charge on C4 can be understood in terms
of a classical resonance picture. The charged nature
of the nitro group simply makes it unfavorable to
place a positive charge at the adjacent carbon. This
idea is illustrated in Scheme 3.
Once the para phenylseleno substituent has been
replaced by a methoxy group, the effect is self-
enhancing because of a substantially higher degree
of stabilization (through overlap between carbon
and oxygen) of a positive charge at a carbon atom
next to a methoxy group (Scheme 4).
This further reduces the tendency for ortho at-
tack. This is inline with the findings for the cor-
responding methanethiolate reaction performed on
2, where exchange of both PhSe-groups utilizing
two equivalents of NaMeS smoothly took place and
only 2,4-bis(methylthio)nitrobenzene 12 could be
observed after reaction (Scheme 1). This meant that
substitution of one PhSe-group in para did not re-
duce the tendency for exchange with NaMeS in
the ortho position. Furthermore, there was no ob-
served ortho/para–selectivity upon reaction of 2 with
a limiting amount of NaSMe. This strengthens the
hypothesis involving the charges on carbon a sulfur-
based species analogous to 2 would be less influ-
enced by the resonance effects shown in Scheme 4.
FIGURE 4 Calculated geometries (B3LYP/6–31G(d)) that
result from the attempts to locate the intermediate Meisen-
heimer complexes in nucleophilic aromatic substitution in
the para (left) and the ortho (right) positions. Only the para
species resembles a Meisenheimer complex.
of the hydroxy groups of a model compound; 2,4-
dihydroxynitrobenzene. The starting guess in these
calculations had C O and C Se distances that are
close to those of regular covalent bonds. This was
done to investigate whether the reason for the re-
sistance against nucleophilic attack of methoxide at
2 in the ortho position is determined by the ener-
getics of an intermediate Meisenheimer complex.
A substantially higher energy of the ortho isomer
over the para would agree with the sole substitu-
tion of the para substitutent. It can be seen from
Fig. 4 that para attack results in a complex, where
˚
the carbon-Se bond is somewhat longer (2.22 A) than
in regular alkylseleno-substituted arenes. This find-
ing contrasts that for the ortho isomer; in that case it
was not possible to optimize a geometry that meets
our expectations on how a Meisenheimer complex
should look regardless of the initial trial structure.
The carbon-Se bond is very long in the case of the
˚
ortho isomer (3.141 A), and the calculated geome-
try more closely resembles a van der Waals complex
of the reactants. The energy of the van der Waals
complex is 18 kcal mol−1 lower than that of the in-
termediate that results from para attack and reflects
the lower energy of the reactants. It seems that the
ortho isomer does not form stable intermediates in
the case of nucleophillic attack.
Charge Distributions in
2,4-Bis(phenylseleno)nitrobenzene and
2-(Phenylseleno)-4-methoxynitrobenzene
Accounting for the Exclusive Para-Substitution
The
charge
distributions
of
the
central
compounds were explored by the calculation
SCHEME 4
Heteroatom Chemistry DOI 10.1002/hc

106 Stuhr-Hansen et al.
We note that the exchange involving NaSMe could
involve free radicals and thus an entirely differ-
ent mechanism. The observation is therefore not an
unequivocal proof.
2,4-Bis(phenylseleno)nitrobenzene 2
To a stirred solution containing diphenyl diselenide
(1.56 g, 5 mmol) and hydrazine hydrate (0.14 g,
2.75 mmol) in DMSO (8 mL) was added 25%
methanolic sodium methoxide (approximately 2 g,
the last 0.2 g added dropwise with intervals of 5 s
until a precise titration end-point yellow to colorless
was reached) in a nitrogen atmosphere. Compound
1 (1.46 g, 5 mmol) was added, and stirring was main-
tained at room temperature for 3 h. The red-brown
reaction mixture was diluted with water (75 mL) and
extracted with ether (3 × 25 mL). The pooled etheral
phases were washed with water (2 × 15 mL), filtered
through alumina (basic, 10 g) by means of ether, and
evaporated. Recrystallization from toluene (80 mL)
and drying in a vacuum oven (60◦C, 1 mBar) gave
2 as yellow crystals; mp 96–97◦C (found: C, 50.18;
H, 3.06; N, 3.14. C18H13NO2Se2 requires C, 49.90; H,
3.02; N, 3.23); 1H NMR (CDCl3): δ 6.77 (d, J = 1.9 Hz,
1 H), 7.08–7.12 (m, 1 H), 7.19–7.32 (m, 5 H), 7.34–
7.41 (m, 3 H), 7.49 (dd, J = 1.4, 6.0 Hz, 2 H), 8.10 (d,
J = 8.5 Hz, 1 H); 13C NMR (CDCl3): δ 125.90, 126.18,
127.28, 129.17, 129.26, 129.35, 129.61, 129.75,
129.78, 129.89, 129.91, 135.73, 136.89, 143.74; 77Se
NMR [10] (CDCl3): δ 450, 497. MS: EI (m/z, relative
intensity): 435 (M+, 100), 388 (7), 342 (30), 308 (18).
CONCLUSIONS
An unusual regioselectivity was observed upon
methoxide exchange of PhSe groups in the
bis(phenylseleno)nitrobenzene 2, forming solely the
product 3 with only the p-PhSe group substituted
with a MeO group, even upon treatment with a
large excess of methoxide. The mechanistic reasons
for the observed regioselectivity are to be found
in the electronic characteristics of the PhSe sub-
stituent. The drawback of using excess of methox-
ide is rapid exchange of PhSe groups in (phenylse-
leno)nitrobenzenes. However, when the NaSePh
reagent is generated from our procedure, it can
be performed as a titration (yellow to colorless)
of diphenyl diselenide with methoxide in the pres-
ence of hydrazine. Diselenides polluted with namely
triselenides and higher selenides can cause an un-
sharp titration end-point, but these species can be
avoided using our procedure. By purification of dis-
elenides via the tosylate salt of the corresponding
seleninic acid [8], unnecessary addition of an ex-
cess of methoxide can be avoided in cases where
this may cause serious damage. It was possible to
obtain X-ray structures of two new ortho (phenylse-
leno)nitrobenzenes 7 and 11, which afforded ad-
ditional information about the nonbonded interac-
tion between the ortho nitro group and selenium,
which resembles a partial five-membered ring since
4-Methoxy-2-(phenylseleno)nitrobenzene 3
Compound 2 (0.87 g, 2 mmol) was suspended in
DMSO (5 mL). Sodium methoxide (5 M in methanol,
1 mL, 5 mmol) was added, and the resulting solu-
tion was stirred for 1 h (at this point of time TLC
showed total consumption of 2). The dark-orange
reaction mixture was diluted with water (15 mL)
and extracted with ether (3 × 10 mL). The combined
etheral phases were washed with water (5 mL), fil-
tered through aluminum oxide (6 g) by means of
ether, and the solvent was evaporated in vacuo (GC-
MS showed no products arising from methoxide sub-
stitution ortho to the nitro group) to give the re-
giospecific product 3 (0.52 g, 84%) identical to the
product synthesized below.
˚
the Se· · ·O distance is 2.65 A, much shorter that the
sum of van der Waals radii. We have verified that the
selectivity is not a result of this interaction.
EXPERIMENTAL
2,4-Dibromonitrobenzene 1
1,3-Dibromobenzene (7.81 g, 33 mmol) was added to
an ice-cooled mixture of concentrated sulfuric acid
(11 mL) and concentrated nitric acid (11 mL) at such
a rate that the temperature was kept at 20◦C. The re-
action mixture was effectively stirred at room tem-
perature for 30 min and then cooled at 0◦C while ice
(25 g) was added in small portions. The yellow pre-
cipitate was filtered off, washed with water and dried
in a vacuum oven (80◦C, 1 mBar). Recrystallization
from hexane (70 mL) afforded 1 (7.93 g, 85%) as
light-yellow needles; mp: 61–62◦C (lit. [9], ref 61◦C);
1H NMR (CDCl3): δ 7.60 (dd, J = 2.0, 8.7 Hz, 1 H),
7.76 (d, J = 8.7 Hz, 1 H), 7.93 (d, J = 2.0 Hz, 1 H).
Unequivocal Synthesis of 3
A sodium phenylselenide solution (1 M in MeOH-
DMSO 1:4, 10 mL, 10 mmol) was prepared by the
standard procedure as a titration at room temper-
ature with a sharp end-point (yellow to colorless).
2-Bromo-4-methoxynitrobenzene (2.32 g, 10 mmol)
was added in one portion. Stirring was maintained
at room temperature for 1 h under nitrogen. The
dark-orange reaction mixture was diluted with water
Heteroatom Chemistry DOI 10.1002/hc

Sparing the Ortho-position in Nucleophilic Aromatic Substitution 107
(70 mL) and extracted with ether (3 × 25 mL). The
combined organic phases were washed with water
(2 × 15 mL), filtered through alumina (neutral, 6 g)
by means of ether, and the solvent evaporated in
vacuo. Recrystallization from hexane (40 mL) and
drying (vacuum oven, 50◦C) gave 3 (2.69 g, 87%)
as yellow crystals; mp 76–77◦C (found: C, 50.89; H,
3.68, N 4.47. C13H11NO3Se requires C, 50.66; H, 3.60;
N, 4.54); mass spectrum (EI; m/z, relative intensity):
tals of 7 and 11 were prepared by slow crystallization
from diluted toluene solutions.
X-ray crystallography
Single crystal X-ray diffraction data were collected
on crystals of compound 7 and 11 cooled to 122.0(5)
K on an Enraf-Nonius CAD4 diffractometer [12],
employing Cu Kα radiation. Data reductions were
performed with the DREAR suite of programs
[13]. All reflections were corrected for background,
Lorentz and polarization effects. Absorption correc-
tions were performed using the numerical Gaussian
integration procedure [14]. The structures were
solved by Patterson and Fourier methods using
SHELXS97 [15] and refined by full matrix least-
1
309 (M+, 100), 248 (7), 232 (9), 216 (93); H-NMR
(CDCl3): δ 3.57 (3H, s), 6.35 (1H, d, J2.7 Hz), 6.72
(1H, dd, J 9.2, 2.7 Hz), 7.42–7.53 (3H, m), 7.67–7.72
(2H, m), 8.19 (1H, d, J 9.2 Hz); 13Se-NMR (CDCl3): δ
55.51, 106.15, 115.88, 124.43, 125.30, 126.42, 128.73,
137.31, 138.24, 168.42; 77Se-NMR (CDCl3): δ 504.
2
squares on |F| -values against all reflections with
2-Methoxynitrobenzene 8 and
4-Methoxynitrobenzene 10
SHELXL97 [16]. The non-hydrogen atoms were
refined with anisotropic displacement parameters.
Positional and isotropic displacement parameters
were refined for all hydrogen atoms. An extinction
parameter was introduced for both refinements.
2-(Phenylseleno)nitrobenzene 7 (0.28 g, 1 mmol,
experiment A) or 4-(phenylseleno)nitrobenzene 9
(0.28 g, 1 mmol, experiment B) were suspended in
DMSO (5 mL). Sodium methoxide (5 M in methanol,
0.24 mL, 1.2 mmol) was added, and the resulting so-
lutions were stirred for 1 h (at this point of time
TLC showed total consumption of the correspond-
ing (phenylseleno)nitrobenzene). Samples for GC-
MS were obtained by quench in water and extrac-
tion with tert-butyl methyl ether. TLC and GC-MS
showed full conversion of starting materials, indi-
cating clean formations of 8 and 10, respectively.
Crystal data for 7. C12H9NO2Se, Mw = 278.16 g
mol−1, crystal dimensions 0.35 × 0.15 × 0.06 mm3,
monoclinic, space group P21/c, a = 9.0947(8),
◦
˚
b= 14.969(3), c = 8.0496(14) A, β = 98.129(11) ,
3
˚
V = 1084.9(3) A , Z = 4, ρcalcd = 1.703
g
cm−3,
μ(Cu Kα) = 4.559 mm−1, 4.91 < θ < 75.90◦, of
8976 measured reflections, 2232 were independent
(Rint = 0.0336) and 2204 observed with I > 2σ(I);
R1 = 0.020, wR2 = 0.0576, GOF = 1.014 for 182 para-
meters, ꢀρmax / min = 0.281/−0.465.
1,3-Dinitro-4,6-bis(phenylseleno)benzene 11
To a sodium selenophenolate solution (20 mmol) in
DMSO (20 mmol) prepared by the standard proce-
dure, 1,3-dibromo-4,6-dinitrobenzene [11] (3.26 g,
10 mmol) was added and stirring was maintained
for 3 h at room temperature under nitrogen. The
dark-orange reaction mixture was diluted with wa-
ter (150 mL) and extracted with ether:toluene (1:2,
3 × 100 mL). The combined organic phases were
washed with water (2 × 40 mL), filtered through
alumina (neutral, 10 g) by means of ether, and
the solvent was evaporated in vacuo. Recrystalliza-
tion from toluene (100 mL) and drying (vacuum
oven, 70◦C) gave 11 (3.49 g, 73%) as yellow crys-
tals; mp 215–216◦C; (found: C 45.19; H 2.48; N 5.84.
C18H12N2O4Se2 requires C 45.21; H 2.53; N 5.86);
mass spectrum (EI; m/z, relative intensity): 480 (M+,
100), 450 (4), 384 (17), 306 (30). 1H NMR (CDCl3): δ
7.34–7.38 (m, 4H), 7.43–7.51 (m, 4H), 7.59–7.64 (m,
2H), 7.98 (s, 1H), 8.92 (s, 1H); 13C NMR (CDCl3):
δ 118.83, 126.57, 128.28, 128.99, 129.32, 131.45,
137.24, 146.25; 77Se-NMR (CDCl3): δ 514. Single crys-
Crystal data for 11. C18H12N2O4Se2, Mw = 478.22
g mol−1, crystal dimensions 0.35 × 0.25 × 0.09 mm3,
orthorhombic, space group Pbca, a = 10.5072(15),
3
˚
˚
b= 27.715(3), c= 11.7420(12) A, V = 3419.4(7) A ,
Z = 8, ρcalcd = 1.858 g cm−3, μ(Cu Kα) = 5.659 mm−1,
3.19 < θ < 74.94◦, of 7713 measured reflections, 3522
were independent (Rint = 0.0292) and 3293 observed
with I > 2σ(I); R1 = 0.0256, wR2 = 0.0677, GOF =
1.137 for 284 parameters, ꢀρmax / min = 0.429/−0.760.
DFT Computations
The geometries and vibrational frequencies were cal-
culated at the B3LYP/6–31G(d) level of theory with
the GAUSSIAN 98 suite of programs [17]. The rela-
tive energies were calculated as the difference be-
tween the sums of the electronic energy and the
zero-point vibrational energy scaled by 1.008 as pre-
scribed by Scott and Radom [18]. Archive entries
Heteroatom Chemistry DOI 10.1002/hc

108 Stuhr-Hansen et al.
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B.; Olmstead, M. M.; Smith, K. M. Tetrahedron Lett
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M. L. A.; Diez, D.; Urones, J. G.; Sanz, F. Tetrahedron
Asymm 2004, 15, 1793.
related to the calculated geometries are available
from the authors upon request.
Supplementary Data
Atomic coordinates, thermal parameters, and bond
lengths and angles for compounds 7 and 11 have
been deposited in the Cambridge Crystallographic
Data Center, CCDC nos. CCDC 703709 and 703710.
Copies of this information may be obtained free
of charge from the Director, CCDC, 2 Union Road,
Cambridge CB2 1EZ, UK on request (fax: +44–1223–
336–033; E-mail: deposit@ccdc.cam.ac.uk or URL:
http://www.ccdc.cam.ac.uk).
[6] Behagel, O.; Mu¨ller, W. Chem Ber 1935, 68, 1540.
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ACKNOWLEDGMENTS
[13] Blessing, R. H. Crystallogr Rev 1987, 1, 3.
[14] DeTitta, G. T. J Appl Crystallogr 1985, 18, 75.
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[16] Sheldrick, G. M. SHELXL-97, Program for the
Refinement of Crystal Structures, University of
Go¨ttingen, Germany, 1997.
We wish to thank Mr. Flemming Hansen for
help with crystallographic experiments. The author
HOS acknowledge the support from the EU Sixth
Framework Programme TotalCryst and the Danish
National Research Foundation.
[17] Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuse-
ria, G. E.; Robb, M. A.; Cheeseman, J. R.; Zakrewski,
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Heteroatom Chemistry DOI 10.1002/hc